1. Technical Field
The present invention relates to a developing device for use in an image forming apparatus, and more particularly, to a developing device for use in an image forming apparatus having a toner cartridge control device capable of controlling the number of replacement times of a toner cartridge relative to the developing device.
2. Background Art
In an image forming apparatus such as, for example, a copier, a printer, an a facsimile machine or other image creation mechanism using an electrophotographic process, a latent image formed on a photosensitive drum (i.e., photo sensitometer) is developed by applying toner from a developing unit onto the photosensitive drum. The developed image is then transferred and fixed onto a sheet of paper. It is common that a replaceable tone cartridge is used to supply toner to the developing unit. During the fixing of each image onto the sheet of paper however, the residue of the toner remains on a surface of the photosensitive drum. Therefore, the residue or waste toner remaining on the photosensitive drum must be collected after cleaning before the photosensitive drum prepares for a next image forming operation.
Generally, there are three conventional processes for collecting and handling residue toner in an image forming apparatus. The first residue toner collection process involves the collection of the residue toner in a container that has to be manually handled. In doing so, the container for storing residue or waste toner has to be specially handled in consideration of environmental conservation. Furthermore, the user must guard against contamination of the interior of the image forming apparatus. That is, unless the user faithfully replaces the container periodically in accordance with a prearranged exchange cycle, generally determined by the manufacturer and based on the size of the container, the residue toner collected by the container overflows from the container and contaminates the interior of the image forming apparatus.
The second residue toner collection process requires the image forming apparatus to circulate by way of electromagnetic and reuse the residue toner. This second method however requires a complex collection device to collect and reuse the residue toner, which imposes undesirable additional costs on the product.
The third process allows the user to keep the collected residue toner inside the developing device, either by using a disposable developing device (called a single cartridge method) or by reusing the same developing device until it wears out, while replenishing the developing device with toner (called a refill cartridge method). In other words, an image forming apparatus is initially provided, e.g., by the manufacturer, with the toner cartridge having toner of a sufficient quantity, or with the toner cartridge having toner that may be replenished by the user on an as-needed basis.
Most conventional image forming apparatuses available in the market adopt the third process for keeping the collected residue toner inside the developing device such as, for example, mentioned U.S. Pat. No. 5,289,243 for Installation And Removal Structure Of A Developing Unit And A Toner Cartridge In An Image Forming Apparatus issued to Sakamoto and U.S. Pat. No. 5,268,722 for Detachable Developer Supply Container Having Means For Selectively Prohibiting Detachment issued to Ikkatai et al. In these conventional apparatuses a toner cartridge is replaced while in the developing unit, and the service life of the developing device must be determined according to the service life of the toner cartridge used and the volume of a storage reservoir collecting residue toner after each image formation operation. Otherwise, the residue toner collected in the storage reservoir may leak out from the reservoir and contaminate the interior of the image forming apparatus.
In order to attempt to prevent leakage of the residue toner collected in the storage reservoir that may contaminate the interior of the image forming apparatus, U.S. Pat. No. 5,229,824 for Developer Material Supplying Device For Integral Type Processing Unit Assembled In Electrophotophic Type Image Recording Apparatus issued to Tsusaka et al. employs a counter in a developing unit for counting the number of replacement times of a toner cartridge so that the user can acknowledge the replacement timing of the developing unit and the storage reservoir. In this construction it is however, difficult to consistently monitor the counter and memorize the exchange cycle of the toner cartridge. Tsusaka '824 uses a toner cartridge limiting mechanism fixed to a developing unit having a movable segment in which, upon application of force by the user, the mechanism allows the user to replace of toner cartridge a fixed number of times. While the toner cartridge limiting mechanism of Tsusaka '824 limits the replacement times of the toner cartridges in an effort to avoid overflow of residue toner contained in the storage reservoir, it has been my observation that the Tsusaka mechanism is readily susceptible to a user's frequent mistake in that if excessive force is applied to the movable segment by accident, for example, the toner cartridge limiting mechanism would fail to allow further toner cartridge replacement even when the storage reservoir is still capable of collecting residue toner from additional toner cartridges without having an overflow or leakage.